Question: 3 crayons cost $5.25. Which equation would help determine the cost of 12 crayons?
There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 12 crayons. Since 12 crayons cost $x$ , we have the following proportion: $\dfrac{12}{x}$ We can write the fact that 3 crayons cost $5.25 as a proportion: $\dfrac{3}{\$5.25}$ The cost changes along with the number of crayons purchased, and so the two proportions are equivalent. $\dfrac{12}{x} = \dfrac{3}{\$5.25}$